The present invention relates to a hand load sensor that is precise, easily used, and which permits analysis of forces exertable by a hand for evaluation and rehabilitation. In the prior art, measurement of grip and pinch strength has been recognized as being desirable. U.S. Pat. No. 4,674,330 illustrates a sensor with a structure that has a pair of bending beams mounted onto a support, which can be bent toward each other. The beams themselves have strain gauges for sensing the bending moments in the beams, but accuracy is always in question. In particular, assertions stating that forces measured at a constant distance are proportional to forces applied anywhere to the structure are inaccurate given normal application of the sensor. Under normal applications, loads applied to the sensor cause elastic deformation of the structure where the strain gauges are located. This elastic deformation contributes to deflection of associated handles as the load is applied which, in turn, causes the sensor to respond non-linearally. In addition, elastic deformation causes twisting moments to appear that are not fully isolated by the strain gauges, while mechanical joints, such as interconnections of the handles with a slider, introduce hysteresis and non-repeatability to the sensor's performance.
A simplified exercising machine which provides gripping or pinching exercises is shown in U.S. Pat. No. 1,007,410. It is designed primarily as an exercise device for piano players. A design patent showing a hand dynamometer is U.S. Pat. No. 247,553 which has a type of indicator dial, and what appears to be a pair of handles that can be squeezed together. A force measuring instrument which can be grasped and used for measuring forces through hydraulic pressure is shown in U.S. Pat. No. 2,708,367. An electric dynamometer utilizing strain gauges on a centrally mounted beam for measuring grasping force between two parallel handles is shown in U.S. Pat. No. 3,442,132.
U.S. Pat. No. 3,672,219 illustrates a grasping device that also operates on a hydraulic principal and displays measured force leads on a gauge. While the hydraulic type gauges eliminate mechanical pivots, they generally are large, not particularly accurate, and they are subject to problems that are associated with leakage of hydraulic fluid.
A hand grip testing machine that can be used as an amusement device, and which utilizes mechanical links shown in U.S. Pat. No. 1,903,352. Other patents which illustrate the general state of the art include U.S. Pat. Nos. 4,530,496; 3,738,651; 1,796,216; 3,916,537 and 4,426,884. These patents show various types of force sensors, but none of these show the unique mounting structure of the present invention which provides for a wide range of force determinations with high accuracy, good repeatability, and little zero shift.